Given the vast breadth of experiences and motivations, I'm hesitant to describe being transgender as intersex. If the focus is narrowed to transsexual people then I'm still incredibly hesitant since, after reviewing relevant studies that I can find, it's my personal belief that the aetiology of gender incongruence hasn't been ascertained. I appreciate that a lot of trans people believe that neuroanatomical evidence has demonstrated a biological origin but I've personally found such work deeply flawed or insufficient to justify generalised claims. Flowing from that, I don't feel the extant evidence I've seen justifies me using the intersex label.
Most importantly for me, I'm also hesitant to accept applying the term at present because I don't want to risk harming the intersex community by appropriating or erasing their unique experiences and challenges. While I understand that appeals to nature are powerful, if illogical, and that it could be wonderful to appease cisnormative society by ascribing gender identity differences to a cause definitively outside of anybody's conscious control, I worry that some dyadic trans people might use intersex people as a political tool. Specifically, I'm concerned that intersex experiences and existence are used to appeal to society's overarching biological essentialism and that by doing so the dyadic trans community can sometimes use and speak over the intersex community in an objectionable manner.
For me, it has potential to be somewhat akin to the way in which the unique suffering of trans women of colour is removed from context and generalised to the whole trans community by some activists. Alternatively, I'd suggest it could be seen as similar to the way in which some organisations use the unique discrimination faced by trans people as a persuasive tool by generalising it to 'LGBT' people in campaigning that overwhelmingly serves the G.
Of course, I understand that my worries could be absurd or excessively cautious. Equally, I'm not saying that dyadic trans people and intersex, cis or trans, people are wildly divergent either since I believe there's significant overlap. The rights of both groups seem to focus on gaining the right to bodily integrity, personal autonomy, medical treatment with informed consent, and liberation from the imposition of deeply cruel models of gender or sex.
As for whether I see being transgender as a birth defect, a large part of me wants to agree that I am defective since being trans has caused so much pain from childhood onwards. However, another part believes that the harm has largely, but not entirely, come from external sources that imposed gender and sex assignment as destiny rather than my own identity so it is society that is defective for placing those baseless concepts above creating maximum happiness, not me.
Similarly, I think trans people are vital or precious rather than defective since I believe persistent outliers undermine systems that can't explain them, trans people challenge prevailing thought by requiring the creation of a new paradigm that embraces us. Flowing from that, I hope trans people that choose to engage in activism or to live openly will be vital in helping to liberate humanity from oppressive gender and sex constructs because I'd argue our very existence proves that many dominant assumptions and expectations are fundamentally wrong. That's probably a bit too optimistic, isn't it? Hehe!